West-side story vs. Grease

I am going to compare the song America from West-side story to the song Beaty School Drop-out from the musical Grease.
Both songs start as if one is talking with some background music. After a little a background voices rise and the song then sarts to have a strong rhythm. And this process repeats a few times.
The song America is more rhythmic that Beauty School Drop-out.
The main instruments in the song America are: (from what I can hear)

• Piano
• Trombones
• And to give rhythm the drums

Meanwhile, the main instrument in Beauty School Dop-out is the piano.